The present invention relates to flame retardant styrenic resin compositions which are environmentally friendly and have excellent flame retardancy without using a halogen-containing flame retardant. More particularly, the present invention relates to a flame retardant styrenic resin composition employing an oxaphospholane compound in the blend of a rubber-modified polystyrene resin and polyphenylene ether resin.
Styrenic resin has excellent mold processability and mechanical properties so the resin has been widely used in electrical appliances. However the styrenic resin is extremely flammable. Therefore, the resin is subjected to various mandatory controls on their flammability in United States, Japan and Europe and is required to have high flame retardancy to meet the Underwriter""s Laboratories Standard for the use of the housing of electrical appliances.
A widely known method for flame retardancy is the addition of a halogen-containing compound or an antimony-containing compound to a rubber modified styrene-containing resin to impart flame retardance. The examples of the halogen-containing compounds used in the method above are, for example, polybromodiphenyl ether, tetrabromobisphenol-A, epoxy compounds substituted by bromine, chlorinated polyethylene, etc. An antimony trioxide or an antimony pentaoxide is commonly used as an antimony-containing compound.
The methods for improving the flame-retardant property by applying a halogen- and antimony-containing compound have advantages such as easy acquisition of flame retardance and no degradation of the physical properties. However, it was observed that the halogen-containing compound resulted in the corrosion of the mold itself by the hydrogen halide gases released during the molding process. Also, these toxic gases are liberated in case of fire. Since a polybromodiphenyl ether, mainly used as a halogen-containing flame retardant, can produce toxic gases such as dioxin or furan during combustion, a major concern in this field is to develop a flame retardant which is prepared without a halogen-containing compound.
A method which employs a mono phosphoric acid ester compound such as triphenyl phosphate as a flame retardant without a halogen-containing compound, is known in the art. U.S. Pat. No. 3,639,506 and German Patent Laid-Open No. 27 51 496 disclose a resin composition wherein an aromatic phosphoric acid ester compound can be used as a flame retardant for a base resin comprised a styrenic resin and a polyphenylene ether resin.
U.S. Pat. No. 4,526,917 discloses that TPP and a mono phosphoric acid ester compound having a mesityl group are added to a base resin comprised a polyphenylene ether resin and a styrenic resin. However, the amount of polyphenylene ether is increased to improve a flame retardancy, so a flowability of the resin composition is decreased.
U.S. Pat. No. 4,503,178 disclosed cyclic phosphine oxides that are useful as flame retardants for styrene modified polyphenylene ether resins. Cyclic phosphinyl-carboxylic acid derivatives are not disclosed.
U.S. Pat. No. 4,081,463 relates to the production of 2-carboxyethyl(phenyl)phosphinic acid which is useful as a flame retardant with organic polymers such as polyester.
U.S. Pat. No. 5,334,760 discloses that a ring-opened oxaphospholane can be used as a flame retardant for polyester. A phosphinyl-carboxylic acid derivative in the form of a cyclic acid anhydride is also disclosed. The flame retardants are disclosed as being useful for polyester.
German Patent Laid-Open No. 28 36 771 discloses that a cyclic phosphate can be used as a flame retardant. The cyclic phosphate does not contain any carboxylic acid portion.
The present invention provides flame retardant styrenic resin composition which have good flame retardancy by using a non-halogen flame retardants and are suitable for the housing of electrical appliances. The resin composition of the present invention can be prepared by employing an oxaphospholane compound as a non-halogen flame retardant to a base resin comprised of rubber modified polystyrene resin and polyphenylene ether. The resin compositions according to the present invention are environmentally friendly and flame retardant with good mold processability and mechanical properties useful for the housing of electric appliances
A flame retardant thermoplastic resin composition according to the present invention comprises
(A) about 5-95 parts by weight of a rubber-modified polystyrene resin,
(B) about 95-5 parts by weight of polyphenylene ether, and
(C) about 1-25 parts by weight of oxaphospholane compound based on 100 parts by weight of the sum of (A) and (B).